A 3rd Generation Partnership Project Long Term Evolution (3GPP LTE) communication system (hereinafter referred to as an “LTE system” for convenience of description) will hereinafter be described as an example of a mobile communication system applicable to the present invention.
A frame structure for use in the LTE system will hereinafter be described. The LTE system supports a type 1 radio frame structure applicable to frequency division duplex (FDD), and a type 2 radio frame structure applicable to time division duplex (TDD).
FIG. 1 shows a structure of a type 1 radio frame used in the LTE system. The type 1 radio frame includes 10 subframes, each of which consists of two slots. A time length of each constituent unit is shown in FIG. 1.
FIG. 2 shows a structure of a type 2 radio frame used in the LTE system. The type 2 radio frame includes two half-frames, each of which is composed of five subframes, a downlink piloting time slot (DwPTS), a guard period (GP), and an uplink piloting time slot (UpPTS), in which one subframe consists of two slots. That is, one subframe is composed of two slots irrespective of the radio frame type. A time length of each constituent unit is shown in FIG. 2.
A resource grid structure for use in the LTE system will hereinafter be described in detail.
FIG. 3 shows an uplink (UL) time-frequency resource grid structure for use in the 3GPP LTE system.
Referring to FIG. 3, an uplink signal transmitted from each slot can be described by a resource grid including NRBUL NSCRB subcarriers and NsymbUL Single Carrier—Frequency Division Multiple Access (SC-FDMA) symbols. Here, NRBUL represents the number of resource blocks (RBs) in an uplink, NSCRB represents the number of subcarriers constituting one RB, and NsymbUL represents the number of SC-FDMA symbols in one uplink slot. The number of SC-FDMA symbols contained in one slot may be differently defined according to the length of a Cyclic Prefix (CP) and the spacing between subcarriers.
Each element contained in the resource grid is called a resource element (RE), and can be identified by an index pair (k,l) contained in a slot, where k is an index in a frequency domain and is set to any one of 0, . . . , NRBULNscRB−1, and l is an index in a time domain and is set to any one of 0, . . . , NsymbUL−1.
A Physical Resource Block (PRB) is defined by NsymbUL consecutive SC-FDMA symbols in a time domain and NSCRB consecutive subcarriers in a frequency domain. Therefore, one PRB in an uplink may be composed of NsymbUL×NSCRB resource elements.
FIG. 4 shows a downlink (DL) time-frequency resource grid structure for use in the LTE system.
Referring to FIG. 4, a downlink signal transmitted from each slot can be described by a resource grid including NRBDL NSCRB and NsymbDL OFDM symbols. Here, NRBDL represents the number of resource blocks (RBs) in a downlink, NSCRB represents the number of subcarriers constituting one RB, and NsymbDL represents the number of OFDM symbols in one downlink slot. The number of OFDM symbols contained in one slot may be differently defined according to the length of a Cyclic Prefix (CP) and the subcarrier spacing. When transmitting data or information via multiple antennas, one resource grid for each antenna port may be defined.
Each element contained in the resource grid is called a resource element (RE), and can be identified by an index pair (k,l) contained in a slot, where k is an index in a frequency domain and is set to any one of 0, . . . , NRBDLNscRB−1, and l is an index in a time domain and is set to any one of 0, . . . , NsymbDL−1.
Resource blocks (RBs) shown in FIGS. 3 and 4 are used to describe a mapping relationship between certain physical channels and resource elements (REs). The RBs can be classified into physical resource blocks (PRBs) and virtual resource blocks (VRBs). Although the above mapping relationship between the VRBs and the PRBs has been disclosed on a downlink basis, the same mapping relationship may also be applied to an uplink.
One PRB is defined by NsymbDL consecutive OFDM symbols in a time domain and NSCRB consecutive subcarriers in a frequency domain. Therefore, one PRB may be composed of NsymbDL×NSCRB resource elements.
The VRB may have the same size as that of the PRB. Two types of VRBs are defined, the first one being a localized VRB (LVRB) and the second one being a distributed type (DVRB). For each VRB type, a pair of VRBs in two slots of one subframe may assigned a single VRB number nVRB.
The VRB may have the same size as that of the PRB. Two types of VRBs are defined, the first one being a localized VRB (LVRB) and the second one being a distributed VRB (DVRB).
In the LTE system based on an Orthogonal Frequency Division Multiple Access (OFDMA) scheme, a resource area in which each UE is able to transmit or receive data to and from a base station (BS) is allocated from the BS to the UE. In this case, not only a time domain but also a frequency domain must be simultaneously allocated to the UE so as to complete resource allocation.
In a wireless mobile communication system such as the LTE system, the time-frequency resources include the above-mentioned resource blocks. A data channel or a control channel is allocated to a certain area of the above time-frequency resources, and is then transmitted and/or received. In this case, if it is assumed that the time-frequency resources allocated to a control channel are limited, information of the control channel can be transmitted at a lower coding rate as the amount of information allocated to the limited resources becomes lowered. As a result, a reception error rate of the control channel can be further lowered.